Field of Invention
This invention pertains generally to combustion engines and, more particularly, to a split cycle engine that runs on gaseous fuels such as natural gas and synthesis gas (syngas) and to a method of operating the same.
Related Art
Even though natural gas and synthesis gas (syngas) may be available in abundant supply, they are often not used as fuel for Otto cycle and diesel engines because of problems such as predetonation. In order to avoid knocking and serious damage resulting from predetonation, engines running on these fuels are sometimes detuned and run on lower compression ratios. However, since the efficiency of the engine is directly related to the compression ratio, reducing the compression ratio can significantly impact the efficiency of an engine. For example, reducing the compression ratio from 16:1 to 9:1 in a diesel engine causes a reduction in efficiency on the order of 30%.
Syngas is made by gasification of biomass and fossil fuels, and the properties of syngas vary with each type of feedstock used. This complicates the problem and can also require compression to be kept at a lower level. The properties of natural gas also change with time as wells produce less oil and the concentrations of water, oil, methane, and other gases vary. Consequently, present engines are inefficient and dirty.
Using detuned diesel engines also creates a large amount of particles, soot, smoke, and other pollutants. Some jurisdictions currently provide air pollution exemptions for such engines because they think that burning the biomass from which the fuels are made would produce even more pollutants. It is strongly believed that if an improved technology were demonstrated, these exemptions would be eliminated, and all future engines would be required to comply with strict air pollution standards already enacted as law.
U.S. Pat. No. 7,481,189 and a number of others issued to the inventor herein introduce internal and external combustion engines having separate compression, combustion, and expansion chambers. These split cycle engines have a number of advantages over conventional diesel and Otto cycle engines, including greater efficiency, the ability to run extremely cleanly without any costly or complicated after treatment, and the ability to run on different fuels without changes in power or cleanliness. However, with gaseous fuels such as natural gas and syngas, great volumes of gas have to be injected at high pressures (e.g., in the range of 500 to 5,000 psi), and the work required to inject the large volumes at high pressure is problematical.
In order to avoid the excessive work required to inject large volumes of gas at high pressure into the engine, diesel manufactures have been sucking the gas into the air intake of the engine, sometimes with the aid of a turbocharger or blower. However, this can also cause predetonation or knocking which can quickly and permanently damage the engine.